This invention relates to control rods to be arranged in a nuclear reactor core, each control rod being provided with supporting pins for supporting control rod guide rollers and fixing members to be secured to the control rod and engaged with the supporting pins thereby preventing the rotation thereof.
In a nuclear reactor core, control rods are located for regulating and distributing power generated in the nuclear reactor. As shown in FIG. 1, each control rod 3 is generally provided with four control rod guide rollers 1 supported by supporting pins 2 at upper and lower portions, respectively, of the control rod 3 so that the control rod will be exactly and smoothly inserted into or withdrawn from the reactor core.
Generally, the control rod guide roller supporting pins 2 are made of a cobalt-based alloy which is hardened by cold working and aging treatment and are directly welded to the control rod 3 as shown in FIGS. 2a through 2d and designated by reference numeral 4 in view of the fact that the supporting pins 2 are slidably engaged with the control rod guide roller 1 under friction.
However, in such a case as described above, since the supporting pin 2 is directly welded to the control rod 3, welding heat transfers to the internal central portion of the pin 2, thus softening the pin itself, degrading the quality of the material thereof as well as increasing the possibility of cracks due to corrosion and strain. The exact control of the amount of the welding heat is considerably difficult in practice.